feat: implement webhook workflow engine for mention-to-audio pipeline

src/lib/engine.js

@@ -0,0 +1,150 @@
+"use strict";
+
+const { WalletStore } = require("./wallet");
+const { AudioAccessStore } = require("./access");
+const { calculateCredits } = require("./credits");
+const { extractArticleFromParent } = require("./article");
+
+class XArtAudioEngine {
+  constructor({ creditConfig }) {
+    this.creditConfig = creditConfig;
+    this.wallets = new WalletStore();
+    this.access = new AudioAccessStore();
+
+    this.jobs = new Map();
+    this.assets = new Map();
+    this.mentions = new Map();
+
+    this.nextJobId = 1;
+    this.nextAssetId = 1;
+  }
+
+  topUpCredits(userId, amount, idempotencyKey) {
+    return this.wallets.applyTransaction({
+      userId,
+      type: "credit",
+      amount,
+      reason: "topup",
+      idempotencyKey,
+    });
+  }
+
+  processMention({ mentionPostId, callerUserId, parentPost }) {
+    if (!mentionPostId) {
+      throw new Error("mention_post_id_required");
+    }
+
+    if (!callerUserId) {
+      throw new Error("caller_user_id_required");
+    }
+
+    const previousJobId = this.mentions.get(mentionPostId);
+    if (previousJobId) {
+      return {
+        ok: true,
+        deduped: true,
+        job: this.jobs.get(previousJobId),
+      };
+    }
+
+    const articleResult = extractArticleFromParent(parentPost);
+    if (!articleResult.ok) {
+      return {
+        ok: false,
+        status: "not_article",
+        reason: articleResult.error,
+        message: "This parent post is not an X Article.",
+      };
+    }
+
+    const creditsNeeded = calculateCredits(articleResult.article.charCount, this.creditConfig);
+
+    const jobId = String(this.nextJobId++);
+
+    this.wallets.applyTransaction({
+      userId: callerUserId,
+      type: "debit",
+      amount: creditsNeeded,
+      reason: "article_generation",
+      idempotencyKey: `mention:${mentionPostId}:charge`,
+    });
+
+    const assetId = String(this.nextAssetId++);
+    const audioText = articleResult.article.content;
+    const fakeAudioBytes = Buffer.byteLength(audioText, "utf8");
+
+    const asset = {
+      id: assetId,
+      ownerUserId: callerUserId,
+      creditsCharged: creditsNeeded,
+      articleTitle: articleResult.article.title,
+      storageKey: `audio/${assetId}.mp3`,
+      durationSec: Math.max(10, Math.ceil(audioText.length / 20)),
+      sizeBytes: fakeAudioBytes,
+      createdAt: new Date().toISOString(),
+    };
+
+    const job = {
+      id: jobId,
+      mentionPostId,
+      callerUserId,
+      status: "completed",
+      creditsCharged: creditsNeeded,
+      article: articleResult.article,
+      assetId,
+      createdAt: new Date().toISOString(),
+    };
+
+    this.assets.set(assetId, asset);
+    this.jobs.set(jobId, job);
+    this.mentions.set(mentionPostId, jobId);
+
+    this.access.grantAccess(assetId, callerUserId);
+
+    return {
+      ok: true,
+      deduped: false,
+      job,
+      reply: {
+        message: `Your audiobook is ready: /audio/${assetId}`,
+        publicLink: `/audio/${assetId}`,
+      },
+    };
+  }
+
+  getWalletBalance(userId) {
+    return this.wallets.getBalance(userId);
+  }
+
+  getJob(jobId) {
+    return this.jobs.get(jobId) || null;
+  }
+
+  getAsset(assetId) {
+    return this.assets.get(String(assetId)) || null;
+  }
+
+  checkAudioAccess(assetId, userId) {
+    const audio = this.getAsset(assetId);
+    if (!audio) {
+      return { allowed: false, reason: "not_found" };
+    }
+    return this.access.canAccess({ audio, userId });
+  }
+
+  unlockAudio(assetId, userId) {
+    const audio = this.getAsset(assetId);
+    if (!audio) {
+      throw new Error("audio_not_found");
+    }
+    return this.access.unlockWithCredits({
+      audio,
+      userId,
+      wallet: this.wallets,
+    });
+  }
+}
+
+module.exports = {
+  XArtAudioEngine,
+};